When we install NGUI in our game it contains some built in Atlas such as - Fantasy, Refractive, SciFi, Wooden. We use them to create buttons, image buttons, progress bar, popup list, scroll bar etc., in which we can only use the images which are used in those atlas.
If we want to use our own Image then we have to create our own custom Atlas.
Here are the steps to create Custom Atlas given below:
Open Atlas Maker
Atlas Maker window will appear
Now set the name of the atlas whatever you like, then select the images in the project window which you want to add in the atlas. after selecting the images they will appear in the Atlas Maker window.
Now click on the green create button to create the atlas.